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  Systems and methods for improving belt motion and color registration in an image forming deviceUSPTO Application #: 20080089703Title: Systems and methods for improving belt motion and color registration in an image forming device Abstract: A method and system of correcting a medium velocity error in a photoreceptor belt of an image forming device with a controller, including measuring a velocity error of the photoreceptor belt when the medium is used in the image forming device, the velocity error comprising a velocity error due to the image forming device dynamics and a velocity error due to torque disturbance on the photoreceptor belt, filtering high frequency velocity error from the measured velocity error, removing the velocity error due to the image forming device dynamics from the measured velocity error to produce a remaining velocity error, converting the remaining velocity error to torque disturbance, determining a correction factor on the basis of the torque disturbance, and correcting the medium velocity factor on the basis of the determined correction factor. (end of abstract) Agent: Oliff & Berridge, PLC. - Alexandria, VA, US Inventor: James Patrick CALAMITA USPTO Applicaton #: 20080089703 - Class: 399 36 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080089703. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001]This disclosure is directed to systems and methods for measuring belt velocity error and reducing torque disturbance in the photoreceptor of image forming devices. [0002]A variety of systems and methods are conventionally used for velocity control in image forming devices. Such systems and methods can include classically designed velocity feedback systems supplemented by a periodic feed-forward control scheme, and feed-forward control algorithms that compensate for an acoustic transfer assist (ATA) vacuum, or drag on the belt, that are disturbed as the belt seam passes over the ATA. This generally involves measuring the transient in belt velocity that is caused by the temporary loss of drag, and commanding the photoreceptor drive motor in a fashion contrary to and simultaneous to the loss in drag. Such a feed-forward control scheme is generally highly effective because the position of the transient is constant, can be tracked as a function of belt position, and varies slowly over time. Moreover, the shape and nature of this disturbance is generally in the form of sin.sup.3, so only the height, width and start point of the correction needs to be known. [0003]FIGS. 1 and 2 illustrate a side elevation view and a front elevation view, respectively, of a schematic of a transfer subsystem 100, which includes a photoreceptor belt 110. A photoreceptor belt motor drive unit 122 engages the photoreceptor belt 110 and moves the photoreceptor belt 110 across a series of support rollers 124, 130, 132, 134, 142, 144, 146, and/or a plurality of non-rotating support bars 152, 154, 156, 158. [0004]Typically, photoreceptor belts are fabricated from long sheets of photoreceptor material that are cut to size. The ends of the cut photoreceptor material are welded, or otherwise mated, together in order to form a continuous belt. This fabrication process produces a photoreceptor belt seam 115 at the point where the ends of the photoreceptor belt 110 are welded, or otherwise mated, to be joined together. [0005]Some transfer subsystems, such as the one shown in FIGS. 1 and 2, include an ATA module 120, which draws the photoreceptor belt 110 into a plenum using a vacuum. The ATA module 120 vibrates the photoreceptor belt 110 in the plenum to aid in transferring toner from the photoreceptor belt 110 to an image receiving medium. [0006]In areas of the photoreceptor belt 110 where there is no seam, a tight vacuum is maintained in the ATA module 120. However, when the photoreceptor belt seam 115 of the photoreceptor belt 110 crosses the ATA module 120, the vacuum seal is momentarily broken. Drag of the photoreceptor belt 110 on the photoreceptor belt motor drive unit 122 is momentarily reduced causing the photoreceptor belt motor drive unit 122 to speed up. Speed of the photoreceptor belt motor drive unit 122 must generally be tightly controlled. Photoreceptor belt velocity sensors (not shown) sense the increase in velocity of the photoreceptor belt motor drive unit 122. A motor control device reacts to readjust the speed of the photoreceptor belt motor drive unit 122 and the photoreceptor belt 110. [0007]New U.S. patent application entitled "Systems and Methods for Determining Feed Forward Correction Profile For Mechanical Disturbances In Image Forming Devices" by James Calamita, filed on May 10, 2005 under Xerox Docket No. 20041690-US-NP (hereinafter "Docket No. 1690"), which is commonly assigned, teaches a control system to automate and/or adapt feed-forward correction (FFC) profile to match precisely the timing and nature of a torque disturbance in a transfer subsystem, which may reduce or substantially nullify torque disturbances, such as, for example, torque disturbances caused by a photoreceptor belt seam passing over an ATA in a photoreceptor belt-based transfer subsystem in an electrophotographic and/or xerographic image forming device. Docket No. 1690 also provides a learning algorithm using a correlated model of system dynamics to compensate for torque disturbances in mechanical systems, such as, for example, transfer subsystems, in image forming devices. [0008]New U.S. patent application entitled "Systems and Methods for Reducing Torque Disturbance in Devices Having an Endless Belt" by Kevin M. Carolan, filed on May 5, 2005 under Xerox Docket No. 20041368-US-NP (hereinafter "Docket No. 1368"), which is commonly assigned, teaches a control system to compensate for motion disturbances which may cause defects in multi-color output images produced by image forming devices. The disclosed system may include a controller that determines when a torque disturbance is expected to occur and controls the photoreceptor belt motor drive unit with a compensation amount that may be retrieved from a data structure. This compensation amount from the data structure may be adjusted via a gain factor and may be combined with the output of a closed loop compensator at a summation point, to attempt to minimize the misregistration effect produced by the torque disturbance in the output images produced by the image forming device. Docket No. 1368 employs a timing methodology to anticipate the onset of a disturbance and via the controller attempts to insert an opposing profile that causes the photoreceptor belt motor drive unit to generate an opposing torque to substantially nullify the disturbance. Amplitude of a correction profile, corresponding to the amplitude of the disturbance, is manually adjusted to attempt to minimize the effects of the disturbance on the produced output images, for example, the color-to-color registration error. The controller monitors the onset of the disturbance or predicts the onset of the disturbance based on sensed photoreceptor belt position and encoder timing. Correction factors for the current operating state of the transfer subsystem in the image forming device are obtained substantially through a trial and error method. SUMMARY [0009]Another source of disturbance to belt velocity is the image forming medium such as, for example, paper, entering and leaving the transfer area. The disturbance in this case is highly dependent upon the medium size and weight as factors external to the photoreceptor, such as pre-transfer medium path speed and pre-fuser transfer medium speed and transfer baffle entry angle. Because there are a number of different variables that contribute to the transients from the medium, it may be desirable to provide a control algorithm capable of tailoring the correction to the specific machine. [0010]Various exemplary embodiments of the systems and methods provide a method of correcting a medium velocity error in a photoreceptor belt of an image forming device with a controller and associated system. The method can include measuring a velocity error of the photoreceptor belt when the medium is used in the image forming device, the velocity error having a velocity error due to the image forming device dynamics and a velocity error due to torque disturbance on the photoreceptor belt. The method can further include filtering high frequency velocity error from the measured velocity error, removing the velocity error due to the image forming device dynamics from the measured velocity error to produce a remaining velocity error, converting the remaining velocity error to torque disturbance, determining a correction factor on the basis of the torque disturbance, and correcting the medium velocity factor on the basis of the determined correction factor. [0011]A system for correcting a medium velocity error in a photoreceptor belt of an image forming device with a controller is also provided. The system can include a measuring unit that measures a velocity error of the photoreceptor belt when the medium is used in the image forming device, the velocity error having a velocity error due to the image forming device dynamics and a velocity error due to torque disturbance on the photoreceptor belt under control of the controller, a filtering unit that filters high frequency velocity error from the measured velocity error, the controller controlling the removal of the velocity error due to the image forming device dynamics from the measured velocity error to produce a remaining velocity error, the controller controlling the conversion of the remaining velocity error to torque disturbance, the controller controlling the determination of a correction factor on the basis of the torque disturbance, and a velocity correction unit that corrects the medium velocity factor on the basis of the determined correction factor. BRIEF DESCRIPTION OF THE DRAWINGS [0012]Various exemplary embodiments of the systems and methods will be described in detail, with reference to the following figures, wherein: [0013]FIG. 1 illustrates a schematic side elevation view of a transfer subsystem for an image forming device including a seamed photoreceptor belt; [0014]FIG. 2 illustrates a schematic front elevation view of a transfer subsystem for an image forming device including a seamed photoreceptor belt; [0015]FIG. 3 is a flow chart illustrating an exemplary method for implementing a torque disturbance reduction within the transfer subsystem of an image forming device; [0016]FIG. 4 is an illustration of an exemplary system for implementing a torque disturbance reduction within the transfer subsystem of an image forming device; [0017]FIG. 5 is a process flow diagram illustrating a feedback loop calculating the velocity error; and [0018]FIG. 6 is a process flow diagram illustrating a feedback loop adjusting the torque disturbance. DETAILED DESCRIPTION OF EMBODIMENTS [0019]These and other features and advantages are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods. [0020]FIG. 3 is a flow chart illustrating an exemplary method for implementing a torque disturbance reduction within the transfer subsystem of an image forming device. In FIG. 3, the method starts in step S100 and continues to step S110, where the average velocity error of the imaging device is measured. According to various exemplary embodiments, a training run can be performed by using the image forming device to form an image on a medium under conditions mimicking conditions existing during an actual image forming operation such as a print job. Alternatively, if the image forming operation is a long job, the training run may be performed on a portion of the job. During the training run, the velocity error may be measured as a function of belt position, at each sample period of the base photoreceptor controller. For example, measurements of velocity error may be performed every 1.6 ms for a 6 seconds belt revolution, which results in taking about 3750 measurements per revolution of the photoreceptor belt. Also, for example, a seam hole on the photoreceptor belt may be used to trigger the data collection and to designate the start of each photoreceptor belt revolution. According to various exemplary embodiments, several such measurements are taken during a plurality of revolutions of the photoreceptor belt during the training run. Thus, the data measured represents 3750 times the number N of revolutions of the photoreceptor belt during the training run. Next, control continues to step S120. Continue reading... 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